able to survive lower salinities than can their 

 predators and disease-causing organisms. Hence, 

 in some tidal tributaries, oysters thrive in regions 

 where they are sheltered from these pests by low 

 salinity. Natural alterations in salinity distribution 

 have been reportedly followed by increased mor- 

 tality of oysters. It is clear that care must be 

 exercised in the approval of engineering projects 

 or industrial processes that will alter salinity re- 

 gimes in tidal tributaries and lagoons and in their 

 associated wetlands. 



Salinity patterns can be caused to vary from 

 "normal" by alterations in character of freshwater 

 inflow and basin geometry. These are the same 

 factors that produce changes in circulation. In fact, 

 salinity alterations are precursors to changes in 

 density currents. 



Recommendation: For the protection of estuarine 

 organisms, no changes in channels, in the basin geom- 

 etry of the area, or in fresh water inflow should be 

 made that would cause permanent changes in isohaline 

 patterns of more than ±10 percent of the natural 

 variation. 



Currents 



Despite their large volumes, tidal waters, espe- 

 cially those in tributaries of the seas, have special 

 circulatory characteristics that may affect their 

 ability to assimilate wastes. For example, tidal ac- 

 tion slows the already slowed (due to lowered 

 slope and resulting reduced speed of gravity-in- 

 duced flow) seaward movement of water in tidal 

 rivers and streams. This alternate up and down 

 stream movement of the water in the freshwater 

 portion of the tidal tributary is confounding 

 enough in itself (Ketchum, 1950 and 1951; Stom- 

 mel, 1953a, b) but in the estuarine reach, the area 

 where sea salts are noticeable, further complexi- 

 ties often occur (Bowden, 1963; Hargis, 1965; 

 Redfield, 1951). In horizontally and vertically 

 stratified mixing estuaries, there are two streams. 

 The upper stream, fresher and lighter, has a net- 

 flow downstream while the lower stream, saltier 

 and heavier, flows inward or upstream. Since 

 these surface currents and bottom counter-cur- 

 rents often extend far to sea off the mouths of 

 large tidal tributary or estuarine systems, as well as 

 far upstream, significant upstream transport of ma- 

 terials in solution or suspension in the counter- 

 current can occur. These circulatory features are 

 important in the life cycles of many estuarine 

 species. For example, oyster and barnacle setting is 

 related to tidal and nontidal currents (Barlow, 

 1955; Bousfield, 1955; Emery and Stevenson, 

 1957; Hargis, 1966; Ketchum, 1954; Pritchard, 

 1953). Large disturbances of current patterns can 



disrupt the life cycles of estuarine organisms. 

 Hence, projects that alter current patterns should 

 be carefully evaluated and controlled. 



It is possible to alter circulatory patterns in tidal 

 tributaries by (1) changing the quantity, timing, 

 and location of fresh water inflow, (2) changing 

 the geometry of the basin. The former can be ac- 

 complished by construction and operation of reser- 

 voirs above or below the fall line (defined as the 

 uppermost limit of ocean's tidal activity). The 

 latter can be accomplished by shoreline or bottom 

 modification; e.g., drainage, bulkheading and fill- 

 ing, channel dredging, and subaqueous spoU dis- 

 posal or mining. Oyster harvesting practices have 

 been known to produce marked changes in bot- 

 tom geometry (Hargis, 1966). 



Recommendation : In view of the requirements of 

 estuarine organisms and the nature of marine waters, 

 no changes in basin geometry or fresh water inflow 

 should be made in tidal tributaries which will alter 

 current patterns in such a way as to cause adverse 

 effects. 



PH 



Despite the great emphasis given to the impor- 

 tance of pH in the literature, little is known of its 

 direct physiological effects on marine organisms. 

 Its indirect effects, however, are extremely sig- 

 nificant. Even a slight change in pH indicates that 

 the buffering system inherent in sea water has been 

 altered radically and that either a potential or 

 actual carbon dioxide imbalance exists. This im- 

 balance can be deleterious or disastrous to marine 

 life. A second indirect effect is that pH can in- 

 fluence the toxicity of other materials. Cyanide and 

 ammonia, discussed under "Toxicity," are out- 

 standing examples of this kind of action. 



Recommendation: Materials that extend normal ranges 

 of pH at any location by more than ±0.1 pH unit 

 should not be introduced into salt water portions of 

 tidal tributaries or coastal waters. At no time should 

 the introduction of foreign materials cause the pH to 

 be less than 6.7 or greater than 8.5. 



Temperature 



Temperature requirements of marine and estua- 

 rine organisms in the biota of a given region may 

 vary widely. Therefore, if we are to maintain tem- 

 perature favorable to the biota, all important spe- 

 cies, including the most sensitive, must be pro- 

 tected. It has been found that organisms in the 

 intertidal zone vary considerably in their ability 

 to withstand high temperatures. Those in the up- 

 permost areas of the tidal zone generally can with- 



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